<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
      var v;
      console.log(v);
      console.log(typeof v);
      v=3.14
      console.log(v);
      console.log(typeof v);
      v='js';
      console.log(v);
      console.log(typeof v);
      v=true;
      console.log(v);
      console.log(typeof v);
      v=null;
      console.log(v);
      console.log(typeof v);

      var str1 = 'Hello JS and Java';
      console.log(str1.toLowerCase());
      console.log(str1.toUpperCase());
      console.log(str1.indexOf('J'));//6
      console.log(str1.indexOf('JS'));//6
      console.log(str1.indexOf('JS', 9));//-1
      var str2 = 'how are you doing today';
      var array = str2.split(' ');
      console.log(array);
      console.log(array[0]);
      console.log('1:2:3:4'.split(':'));
    </script>
</head>
<body>

</body>
</html>